Ethernet The term Ethernet refers to the family of local-area network (LAN) products covered by the IEEE 802.3 standard that defines what is commonly known as the CSMA/CD protocol. Four data rates are currently defined for operation over optical fiber and twisted-pair cables: 10 Mbps 10Base-T Ethernet 100 Mbps Fast Ethernet 1000 Mbps Gigabit Ethernet 10000 Mbps 10Gigabit Ethernet Source: Cisco
Ethernet Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format. Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been in use from around 1980[1] to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET. In recent years, Wi-Fi, the wireless LAN standardized by IEEE 802.11, is prevalent in home and small office networks and augmenting Ethernet in larger installations Source: Wikipedia
Ethernet A History Ethernet was originally developed at Xerox PARC in 1973 1975. In 1975, Xerox filed a patent application (U.S. Patent: Multipoint data communication system with collision detection). The experimental Ethernet described in that paper ran at 3 Mbit/s, and had 8-bit destination and source address fields, so Ethernet addresses were not the global addresses they are today. By software convention, the 16 bits after the destination and source address fields were a packet type field, but, as the paper says, "different protocols use disjoint sets of packet types", so those were packet types within a given protocol, rather than the packet type in current Ethernet which specifies the protocol being used. Metcalfe left Xerox in 1979 to promote the use of personal computers and local area networks (LANs), forming 3Com. He convinced DEC, Intel, and Xerox to work together to promote Ethernet as a standard, the so-called "DIX" standard, for "Digital/Intel/Xerox"; it standardized the 10 megabits/second Ethernet, with 48-bit destination and source addresses and a global 16-bit type field. The standard was first published on September 30, 1980. It competed with two largely proprietary systems, token ring and ARCNET, but those soon found themselves buried under a tidal wave of Ethernet products. In the process, 3Com became a major company. Twisted-pair Ethernet systems have been developed since the mid-80s, beginning with StarLAN, but becoming widely known with 10BASE-T. These systems replaced the coaxial cable on which early Ethernets were deployed with a system of hubs linked with unshielded twisted pair (UTP), ultimately replacing the CSMA/CD scheme in favor of a switched full duplex system offering higher performance.
Ethernet interface card (coaxial- and twisted pair based)
Ethernet - A general description Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium. The common cable providing the communication channel was likened to the ether and it was from this reference that the name "Ethernet" was derived. From this simple concept, Ethernet evolved into the complex networking technology that today underlies most LANs. The coaxial cable was replaced with point-to-point links connected by Ethernet hubs and/or switches to reduce installation costs, increase reliability, and enable point-to-point management and troubleshooting. The advent of twisted-pair wiring dramatically lowered installation costs relative to competing technologies. Above the physical layer, Ethernet stations communicate by sending each other data packets, blocks of data that are individually sent and delivered. As with other IEEE 802 LANs, each Ethernet station is given a single 48-bit MAC address, which is used both to specify the destination and the source of each data packet. Network interface cards (NICs) or chips normally do not accept packets addressed to other Ethernet stations. Adapters generally come programmed with a globally unique address. Despite the significant changes in Ethernet from a thick coaxial cable bus running at 10 Mbit/s to point-topoint links running at 1 Gbit/s and beyond, all generations of Ethernet (excluding early experimental versions) share the same frame formats.
CSMA/CD shared medium Ethernet Main procedure: Frame ready for transmission. Is medium idle? If not, wait until it becomes ready and wait the interframe gap period (9.6 µs in 10 Mbit/s Ethernet). Start transmitting. Did a collision occur? If so, go to collision detected procedure. Reset retransmission counters and end frame transmission Collision detected procedure Continue transmission until minimum packet time is reached (jam signal) to ensure that all receivers detect the collision. Increment retransmission counter. Was the maximum number of transmission attempts reached? If so, abort transmission. Calculate and wait random back off period based on number of collisions. Re-enter main procedure at stage 1.
Ethernet framing The Ethernet Version 2 or Ethernet II frame, the so-called DIX frame (named after DEC, Intel, and Xerox); this is the most common today, as it is often used directly by the Internet Protocol.
Ethernet versions Fast Ethernet 100BASE-T -- A term for any of the three standard for 100 Mbit/s Ethernet over twisted pair cable. Includes 100BASE- TX, 100BASE-T4 and 100BASE-T2. 100BASE-TX -- Uses two pairs, but requires cat-5 cable. Similar star-shaped configuration to 10BASE-T. 100 Mbit/s. 100BASE-T4 -- 100 Mbit/s Ethernet over Category 3 cabling (as used for 10BASE-T installations). Uses all four pairs in the cable. Now obsolete, as Category 5 cabling is the norm. Limited to half-duplex. 100BASE-FX -- 100 Mbit/s Ethernet over fibre. Gigabit Ethernet 1000BASE-T -- 1 Gbit/s over cat-5 copper cabling. 1000BASE-SX -- 1 Gbit/s over fiber. 1000BASE-LX -- 1 Gbit/s over fiber. Optimized for longer distances over single-mode fiber. 1000BASE-CX -- A short-haul solution (up to 25m) for running 1 Gbit/s ethernet over special copper cable. Predates 1000BASE-T, and now obsolete. 10 gigabit Ethernet The new 10 gigabit ethernet standard encompasses seven different media types for LAN, MAN and WAN. It is currently specified by a supplementary standard, IEEE 802.3ae, and will be incorporated into a future revision of the IEEE 802.3 standard. 10GBASE-SR -- designed to support short distances over deployed multi-mode fiber cabling, it has a range of between 26 m and 82 m depending on cable type. It also supports 300 m operation over a new 2000 MHz km multi-mode fiber. 10GBASE-LX4 -- uses wavelength division multiplexing to support ranges of between 240 m and 300 m over deployed multi-mode cabling. Also supports 10 km over single-mode fiber. 10GBASE-LR and 10GBASE-ER -- these standards support 10 km and 40 km respectively over single-mode fiber. 10GBASE-SW, 10GBASE-LW and 10GBASE-EW. These varieties use the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment. They correspond at the physical layer to 10GBASE-SR, 10GBASE-LR and 10GBASE-ER respectively, and hence use the same types of fiber and support the same distances. (There is no WAN PHY standard corresponding to 10GBASE-LX4.) 10 gigabit Ethernet is very new, and it remains to be seen which of the standards will gain commercial acceptance.
Ethernet devices Ethernet repeaters and hubs A greater length could be obtained by an Ethernet repeater, which took the signal from one Ethernet cable and repeated it onto another cable Multiport Ethernet repeaters became known as "Ethernet hubs Bridging and switching Ethernet bridges and switches work somewhat like Ethernet hubs, passing all traffic between segments. However, as the switch discovers the addresses associated with each port, it only forwards network traffic to the necessary segments improving overall performance
Review Questions Q Ethernet general description Q Ethernet - collision detected procedure Q Ethernet frame Q Ethernet devices Q Ethernet standards